1. Field of the Invention
The present invention relates to a front light type lighting device adapted to a license plate part of a vehicle, or lightening of many kinds of liquid crystal displays etc. and particularly to an illumination device for the license plate.
2. Related Art
As methods for heightening visibility of a car license plate, there are a method which irradiates light of bulbs positioned above or below the license plate to the surface of the license plate, and a method of using the license plate of a letter lighting system. As to the license plate of the letter lighting system, many improvements are proposed in Japanese Patent Publication Nos. JP H10-129344A, JP 2000-313279A and JP H10-119669A.
Since the light of the bulb employed in the former method is low in directivity, even if the bulb is installed, for example, in opposition to the license plate, some parts of the light emitted from the bulb go to other directions than the license plate. Such lights are not used to illumination of the license plate, besides cause to decrease confirmation of the license plate, and further lower a design property in the portion of the license plate. From the designing viewpoint, it is not desirable that the bulb itself is observed from the outside. Taking the above mentioned into consideration, the surroundings of the bulb other than the side of the license plate are coated with a garnish. On the other hand, for the light from the bulb being easy to irradiate the surface, it is necessary to incline the license plate with respect to the attaching face. In such prior practices, the surroundings of the light sources are coated with the garnish, and the license plate is inclined. As a result, the part of the license plate is inevitably thick along a full length of the car.
On the other hand, also in the license plate of the letter lighting system, it is necessary to secure a space for disposing back lights at the inside of the license plate, and as a whole, an apparatus becomes thick. In addition, owing to necessity of using a specially processed license plate, ordinarily used license plates cannot be utilized and are lack in general purposes. Further, a structure is complicated and high in production cost.
Meanwhile, as for the lighting devices other than the license plate lighting devices, recently, as a lighting way for liquid crystal monitors such as PC (personal computer) or mobile information terminals, a back light system has in general been used. In the back light system, the lighting is practiced by a light from the light guide member installed at a rear side of an illumination object (e.g., liquid crystal). The light guide member for the back light is performed at the back face with a printing or coating in white, or pasted with a reflecting sheet for uniformalizing a light radiated from a front side.
On the other hand, in use of some parts, there has been a practice where the light guide member is disposed at the front face side (an observing face) of the illumination object for lighting by the light radiated from the back face of the light guide member, that is, a practice of the front light. Since this practice interposes the light guide member between an observer and the illumination object, high transparency is demanded to the light guide member itself. Accordingly, the light guide member performed with the white-printing on the upper surface cannot be used like the back light system.